Receptors in brain membranes which mediate the pharmacological effects of the neuroactive peptides bombesin and vasointestinal peptide have been demonstrated by direct binding. The regional and subcellular distributions of these peptide receptors suggest that these receptors are physiologically important and that they mediate important brain functions when they interact with endogenous components present in the central nervous system. Methods for detailed autoradiographic mapping of brain regional distribution of neurotransmitter receptors is being developed.